The present invention relates to methods and apparatus for operating on gases.
The present invention relates in particular to methods and apparatus for carrying out operations such as pumping gases, by means of a liquid, from a lower to a higher pressure, and operations such as altering the extent to which a gas is contained in a liquid.
It is already known to pump gas from a lower to a higher pressure by utilizing a liquid jet ejector, generally employed for such purposes as, for example, pumping gases from a vacuum to normal atmospheric pressure. A vacuum is generated by converting the pressure energy of the liquid into kinetic energy, and thereafter this kinetic energy is reconverted into pressure energy. In practice, when it is desired to achieve a substantial degree of vacuum, it is essential to utilize comparatively high water supply speeds. For example, in water jet ejectors by means of which air is pumped from a pressure of 30 mbar to a normal pressure, the water supply pressure is commonly higher than 300 kN/m.sup.2 and the velocity of water flow in the nozzle is higher than 25 m/s. Inasmuch as even under these conditions the gas mass which is pumped remains comparatively small, on the order of 10.sup.-.sup.4 times the water quantity, the overall efficiency of ejectors of this type is undesirably low, being on the order of 5-8 per cent.
In connection with the extent to which a gas is contained in a liquid, the solubility of gases in liquids is known to behave according to Henry's law, according to which the solubility of a gas in a liquid is proportional to the gas pressure. Thus, if this pressure is reduced, the solubility of the gas decreases and the dissolved gas tends to separate from the liquid.
This latter phenomenon is utilized, for example, in the so-called vacuum deaeration process for separating air which is dissolved in water, and in this process the water is conducted into a tank under vacuum, so that the air separates from the water in the latter tank, and thereafter the air is pumped out of the tank by utilizing a vacuum pump. However, such vacuum pumps operate only with a relatively poor efficiency, and the gases are required to be pumped from relatively low pressures, so that comparatively high costs are involved in such processes.
It is well known that the dissolving of gases in liquids and the separation of gases therefrom usually involve a substantially irreversible process. This is true, for example, in the case of gases which are taken from air and dissolved in water. Separation of such gases from water at a relatively low pressure takes place much more readily than redissolving of such gases into the water. Thus, the relatively slow dissolving of gases in liquids causes difficulties where it is desired to carry out operations such as oxygenation of water. Conventional water oxygenation methods require a considerable excess of air bubbles to be pumped into the water, these air bubbles rising to the surface of the water. Operations of this latter type also involve high costs at the present time.